1. SESAME: Surface Electric Sounding and Acoustic Monitoring Experiment
Rosetta Lander Experiment SESAME Electric and Acoustic Sounding of a Cometary Surface
Web-site:
Publication: K. J. Seidensticker et al., Space Science Reviews (2007) 128:
SESAME: Surface Electric Sounding and Acoustic Monitoring Experiment
DIM: Dust Impact Monitor
Goal
Measure number, direction as well as velocity and size distributions of impacting particles as function of rotational and orbital phase of the cometary nucleus.
SESAME is one of nine experiments on-board the lander Philae of the ESA Rosetta mission (launch: 2. March 2004) that should reach comet 67P/Churyumov-Gerasimenko in SESAME comprises the instruments CASSE, DIM, and PP.
Method
DIM consists of active Piezo sensors mounted on three orthogonally outer side walls of a cube. Impacting particles generate an oscillating damped sinusoidal voltage in the Piezo crystal, the peak amplitude and contact duration of which are measured.
Performance
Velocity: m/s
Radiusa: 5 x x 10-3 m
Energy: 2 x x 10-7 J
Mass: 6 x x 10-4 kg
a Spherical particles with a density of 1000 kg m-3 have been assumed.
Positions of SESAME sensors on the Rosetta lander Philae
DIM sensor cube with the three active Piezo plates visible.
Goal
Measure mechanical and electrical properties of the cometary surface as well as parameters of emitted ice-dust particles. Determine the variations with the rotational and orbital cometary phase.
Budget
Mass (electronics): 900 g
Mass (sensors): 750 g
Power: 2.5 W
Calculated energy limits of ice balls with different radii. Ecomet is the theoretical relationship between expected energy and radius of cometary particles.
Foot -Y of Lander FM with soles (black and green covers) and ice screw (center)
CASSE: Comet Acoustic Surface Sounding Experiment
PP: Permittivity Probe
Goal
Determine the elastic constants (Young’s modulus and Poisson’s ratio) and their variation with time by measuring the velocities of compressional and shear waves.
Monitor the cometary activity and locate external sound sources (impacts, thermal cracking etc.).
Goal
Determine the water ice content of the cometary surface layer and its variation with time
Method
PP uses a quadrupole probe to measure the complex permittivity  of the cometary surface layer by injecting an AC current between two terminals and measuring the induced potential difference and its phase by means of two other terminals.
Method
Active sounding (with Piezo transmitters) and passive acoustic listening is possible with sensors in the soles of Philae.
Performance
Acoustic sensitivity is critically dependent on surface contact
RX frequency range: kHz
A numerical simulation method for porous media is available to support data analysis
6 thermoresistors mounted in soles
Temperature range: -140 … +100°C
Philae sole of leg +Y with PP pre-amplifier on sole cover (left). The glass fiber sole (right) contains the PP electrode mesh as well as a CASSE accelerometer (within mounting).
PP electrode (brown mesh) on MUPUS-PEN
Sole of foot +Y with CASSE trans- mitter (left) and sole cover (right)
Performance
Active:
Sounding frequency: 0.01 to 20 kHz
Determination of water-ice content down to 2 m depth, depending on electrode distance.
Spatial Resolution: 5 to 15 %
Passive:
Power spectrum of plasma waves till 20 kHz
Sound transfer via a frozen Dunite sand bed. Accelerometers were at 40 (ACC1) and 80 cm (ACC2) distance from transmitter.
Sound velocity from cross correlation: 700 ± 60 m/s
Electrode potentials between
MUPUS-PEN and +X foot